The use of pyrophoric gases to deposit process layers on to silicon wafers or flat panel displays is well known. Such gases include silane, disilane, dichlorosilane and trichlorosilane. Pyrophoric gases can pose a risk in that they may cause a spontaneous and uncontrolled pyrophoric reaction on contact with air. In order to minimize the risk of an uncontrolled pyrophoric reaction due to the presence of pyrophoric gases within the waste stream exhaust from the process tool, it is known to employ a “burn box” or “burn tube” to remove the pyrophoric gases to a concentration below flammable limits by causing the pyrophoric gas to react with air. Such burn tube devices generally include a reaction chamber having inlets for receiving the pyrophoric gas-containing stream and a stream of air for producing a controlled and contained pyrophoric reaction within the chamber, and an exhaust duct of conveying the waste stream from the chamber.
When silane, for example burns, large amounts of silica powder are formed, which can rapidly block the reaction chamber, inlets and downstream duct. As a result, regular cleaning of the device is required, which can increase costs and incur downtime of the process tool. In addition, if a fault occurs, the temperature in the device can rapidly rise, posing a potential fire hazard. Furthermore, it has become common practice to dilute the silane bearing gas stream with a diluent gas, typically nitrogen, to a level at which it is not flammable in or immediately behind a pumping mechanism for drawing the waste stream from a process chamber (a level of below 1% is often recommended). Such dilution renders the subsequent use of burn tubes ineffective.
It is an aim of at least the preferred embodiment of the present invention to seek to solve these and other problems.